hoagland



y 1959 K. A. HOAGLAND Re. 24,673

- ELECTROSTATIC ELECTRON LENS Original Filed July 3, 1951 4 sheets-sheet1 Y INVEN TOR. KENNETH A. HOA'GLAND ATTORN E Y8 July 28,1959 K. A.HOAGLANYD I 24,673

ELECTROSTATIC ELECTRON LENS Originai Filed July 3. 1951 4 sheets-sheet z3 KENNETH A. HOAGLAIYD BY PW Q Q A TTORNEYS July-- 28, 1959 KQA.HOAGLAND 24,673

I ELECTROSTATIC ELECTRON LENS Original Filed July 3, 1951 4 Sheets-Sheet5 INVENTOR. KENNETH A. HOAGLAND ATTORNEYS July 28, 1959 K. A. HOAGLANDzuscmos-mrc ELECTRON mus Original Filed July 3, 1951 4 Sheets-Shoot 4 Flg. 8

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a B F 8 6 JEFZUFE INVENTOR. KENNETH A. HOAGLAND Fig.9

A TTORNEYS Re. 24,673 Reissued July 28, 1959 ELECTROSTATIC Kenneth A.Hoa'gland, High Crest Lake, N.J., assiguor to Allen B. Du MontLaboratories, Inc., Clifton, N.J.,

a corporation of Delaware Original No. 2,719,243, dated September 27,1955, Serial No. 235,010, July 3, 1951. December 7, 1956, Serial No.627,087

14 Claims. (Cl. 315-16) Matter enclosed in heavy brackets [I] appears inthe original patent but forms no part of this reissue specification;-matter printed in italics indicates the additions made by reissue.

This invention relates to cathode ray tubes and particularly toelectrostatically focused cathode ray tubes.

Many electrodes configurations have been devised heretofore to provideelectrostatic focusing for the electron beams in cathode ray or othercharged particle tubes.

One example of such configurations is the so-called unipotential lenscommonly used in electrostatically focused television picture tubes.This lens comprises three elements: the tubular second anodes of theelectron gun, usually with a limiting aperture and outwardly flaredskirt at the forward end thereof; a focusing ring electrode having thesame internal diameter as the tubularportion of the second anode; and asecond limiting aperture with an outwardly flaring skirt and usually ashort tubular section; These electrostatic lenses are designed to focusa beam of electrons in the cathode ray tube when a voltage ofapproximately 20% of the anode voltage is applied to the focuselectrode. Therefore, it is necessary to derive a voltage ofapproximately 3,000 v. from some point in the television power supplycircuit to apply' to this electrode for the usual anode voltage of about15,000 v. Since this voltage must vary proportionately'with thevariations in the anode voltage, it is common to provide avoltagedivider from the anode power supply and connect a tap at thedesired voltage level to the focus electrode. However, since it isnecessary to vary the voltage at the focus electrode within a limitedrange in "order to obtain the best possible focus of the spot, a highvoltage potentiometer mus-t be provided which is capable of withstandingpotential difier- 1 ences of 5,000 v. or more.

Tubes have alsobeen devised heretofore in which the focusingelectrodetwas connected directly to the cathode of the tube. Such tubescan then focus only if the parts making the electron lens have thecorrect size and space relationships, and these tubes have beenuneconomical to produce in large quantities because of the many verycritical tolerances involved.

Figure 1. shows a cathode ray tube embodying the invention.

Figure 2- is simplified version, of the tube in Figure 1.

V Figure 3 is a graph showing the variation of the focal :strength oftheelectron lens. 7

Application for reissue Figures 4 and 5 show different embodiments ofthe invention.

Figure 6 shows a typical embodiment of the electron lens.

Figures 7 and 8 are ditferen-t embodiments of the electron lns and v IFigure 9 is a graph illustrating the electrical differences betweenFigures 7 and 8.

In. Figure 1, an electron gun comprising a first grid 11, a second grid12, and an anode 13 is disposed in the neck of a cathode ray tube 14.The anode 13 in this tube may take the form of the bent anode operatingin the nianner described in my cope'nding application Serial No;129,260, or it may take one of a number of alternative forms, as will bedescribed later. The forward end of the anode 13, that is, the endnearest the fluorescent screen or target 16 is covered by a cup-shapedcap 17 which is concave toward the forward end of the tube and containsa central aperture 18. Mounted transversely within the anode 13 is adisc 19 having a central aperture20'which is preferably somewhat smallerin diameter than the aperture 18.

The tubular electrode 21 coaxial with the forward portion of the anode13 is rigidly secured thereto by a mounting structure comprising aplurality of support pins 123 having their inner ends welded to theelectrodes and their outer ends heldby glass rods 22 as described incopending application Serial No. 166,401 to Eric Pohle, assigned to thesame assignee. A tubular field-defining electrode 24 electricallyconnected to anode 13 is similarly secured in axial alignment withthe-electrode 21 and the the tube 14 by a radially extending member 29with spring in Figure l. ,are electrically connected together and thefocusing elecclips 31 attached thereto to make electrical and mechanicalcontact with a conductive coating 32 on the inner wall of the neck ofthe cathode ray tube 14 as described in copending application Serial No.200,469 by Herndon W. Leighton, assigned to the same assignee. Otherresilient supports may, of course, be substituted, and they need notnecessarily be attached to electrode 24.

The electrical action of an electron gun similar to the one shown inFigure 1 will be illustrated now with ref- I erence to Figure 2. Theelectron gun shown in Figure 2 ,the straight electron gun shown here orthe bent gun of Figure; 1. or the well known slashed-field gun, tiltedgun,

oif set gun, or any combination of these guns which will produce therequired beam of electrons. To the right of line 33 is the electrostaticelectron lens which forms the subject of this application and may beconstructed in any of several forms, examples of which will be describedhereinafter. Each of the examples to be described will consist of ananode similar to anode in Figure 1, a focusing electrode 21 having alarger internal diameter than the external diameter of the end of theanode, and a field-defining electrode such as electrode 24 The anode andthe field-defining electrode trode is directly connected to the constantpotential source such as the cathode of the tube. For the purpose ofthis invention, the voltage on the cathode will be assumed to beconstant although in actual practice the video signal may be connectedthereto. The complete cathode ray tube may be made up with any of thevariations of the electron gun in combination with any of the forms ofelectrostatic electron lens.

The cathode 34, coaxially mounted within the grid 11, emits a stream ofelectrons 36 when heated by the heater 37. This stream is prefocused inthe manner described in the above-mentioned application Serial No.129,260 to form a constricted bundle which impinges on the aperture 20in the disc 19. Not all of the electrons in the beam 36 will passthrough the limiting aperture 20; some will strike the periphery and mayrelease secondary electrons therefrom. These secondary electrons followthe dotted curves 38 and, as may be seen, most of these secondariesstrike the periphery of the aperture 18 in the cap 17. This aperture 18is made somewhat larger than the aperture 20 in order that the mainbundle of electrons will not be impeded in passing therethrough. Most ofthe secondaries which escape the periphery of the aperture 18 will becaptured by the periphery of the aperture 28 in the field-definingelectrode 24.

In accordance with the objects of this invention, the

electron lens structure described herein reduces the numher of criticaldimensional tolerances, the main ones being the diameter A of theelectrode 21 and the distance B between electrodes 13 and 24. In Figure2, the diameter A of the focusing electrode 21 is greater than thediameter of the anode 13 by an amount 2D and the electrode 21 overlapsthe electrodes 13 and 24, each by an amount C. It has been found that ifC is equal to D, very good focal properties result although otherrelationships may work equally Well. One reason for this is believed tobe that the overlap by the electrode 21 excludes stray fields from theelectron lens region. Lenses in which the diameters of the anode 13 andthe field-defining electrode 24 are .500 in. and A is .625" and B is.390" have beeen found to work particularly well although thesedimensions are to be taken only as a sample and should not be construedto limit the invention.

A well known formula for determining the focal strength of auni-potential electron lens such as the one under discussion is m an inwhich F is the focal strength, f the focal length, V the anodepotential, V is the axial potential in the lens region and varies withz, the axial distance, and V is the derivative of V with respect to z. Acurve of F versus the overlap C has been plotted in Figure 3 to show howthe focal strength varies with different amounts of overlap. The curve41 was obtained by cutting equal amounts off each end of the electrode21 and making measurements in an electrolytic tank. It will be seen thatwhen the overlap exceeds zero, which is to say as soon as there is anyoverlap, the curve 41 levels out, and when the overlap exceedsapproximately .040", the focal strength is substantially independent ofany further overlap. Below zero, that is, when there is a positive axialdistance between a plane passed through the end of the anode 21 and aplane passed through the proximal end of either electrode '13 orelectrode 24 (since this positive axial distance will be the same foreither), curve 41 starts to drop very rapidly. This is an indication ofthe critical tolerance of the length of electrode 21, unless there issome overlap.

Curve 42 ditfers from curve 41 in that the overlap was varied only forone end of electrode 21. This curve was obtained by taking an electrode21 of fixed length and moving it axially over either electrode 13 orelectrode 24. Thus, the overlap was increased for the electrode overwhich electrode 21 was telescoped and was correspondingly decreased forthe other electrode (either 13 or 21). As was seen in curve 41, a largeoverlap made very little difference so that curve 42 essentiallyrepresents the variation of the changing overlap at one end only. Ingeneral, the shape of curve 42 is similar to the shape of curve 41, and,as is expected, the focal strength is higher for a given degree ofnegative overlap than curve 41 due to the asymmetrical form of theelectron lens. It should be emphasized that the diameter A of electrode21 and the spacing B between electrodes 13 and 24 are the principaldeterminants of the focal strength of the electron lens, but thesedimensions may be chosen so that the electron lens will focus at anygiven distance no matter what the overlap may be, whether positive ornegative. Therefore, electron lenses, and even automatically focusedlenses, may be designed in which the overlap is negative, but the pricewhich must be paid for such design is an increase in the number ofcritical tolerances of the various parts.

It will be noted that the electrode 24 is electrically connected to thewall coating 32 of the cathode ray tube, and there is, therefore,substantially no lens action at the plane through the forward end of theanode 24. This anode is necessary in order to define the field in thelens region. Prior art electron lenses have been designed in which thewall coating 32 served as part of the field-defining structure in thelens region. Such tubes are critical as to angular displacement of theelectron gun within the neck of the tube, and it is mainly for thisreason that the lens-defining electrode 24 has been added. Since thiselectrode is quite rigidly attached to the anode 13 and the focusingelectrode 21, the components defining the electron lens are fixed intheir spaced relationships during the manufacture of the gun wheretolerances may be easily held to a reasonable amount, instead of beingdependent on the alignment of the gun within the neck of the tube whereit is extremely difficult to hold close tolerances of alignment. Theoverlap .C enters into this discussion since the electrostatic field ofthe wall coating is prevented from extending into the lens region partlyby this overlap. A negative overlap, i.e. lack of any overlap and axialspacebetwcen the ends of the electrodes, permits the field of the wallcoating 32 to have some effect in the lens region in spite of thefield-defining electrode 24 unless some care is taken to keep thecoating 32 well away from the lens region. This effect may be preventedby providing long spring fingers (Figure 4) attached to the skirt 29 ofthe electrode 24 and extending forward to make contact with the end ofthe wall coating 32- which then may be terminated that much furtherforward.

The structure shown makes possible another beneficial result inpreventing electrical leakage, corona or are discharge or breakdownbetween the cylindrical electrodes through a path established on or nearthe supporting members. Referring to Figure 1, it may be seen that thesupporting rods 22 arespaced from the focusing electrode 21 and the twoparts of the anode 13 and 24 by a plurality of metal studs 23. Thesupporting metallic studs 23 making contact with the focusing electrode21 are placed well toward the center thereof. Similarly, the supportingstuds 23 contacting the portions 13 and 24 of the anode are spaced fromthe ends of the focusing electrode 21. This spacing as illustrated at Etogether with the stepped arrangement provided by the larger diameter ofthe focusing electrode 21 as compared with the diameter of the anode 13and 24 increases the clearances and prevents electrical leakage, coronaor are discharge or breakdown therebetween.

' Figure '4 shows the so-called tilted ion-trap comprising the c-athode34, a control grid 11, a second grid 112, and an anode 213. Electronsemitted by the cathode 34 pass through the aperture in the control grid11 and the second grid 112, are deflected forwardly by the asymmetricalelectric field existing between the second grid 112 and the anode 213,and are subsequently deflected by a magnetic field indicated by thedotted region 44. Since the axis of the electron gun is normally at anangle of approximately twoor three degrees with respect to the axis ofthe tube 14 (this small angle is greatly en- 55 l larg'ed "here forpur'pos'esbf illustration), 'the deflection by the magnetic field 44causes the electron beam 136 to travel substantially along'the axis ofthe tube 14. These electrons then enter the lens region to the right ofline 33 substantially in alignment with the axis and subsequent forceson these electrons by the lens structure comprising the focusingelectrode 21 and field defining electrode 24 are as described inconnection with Figure 2, The small angle which the electron gun sectionto the left of line 33 makes with the axis of the lens section totheright of line 33 does not materially alter the focal properties ofthe lens and hereinafter, in the specification and claims, the termsubstantially aligned" will 'be used to indicate structures such as thatin Figure 4 as well as those in .Figures 1 and 2. 7

Another modification of the invention is shown in Figure 5. The focuslens axis preferably should coincide with the forward portion of theanode 13 when the Ebent gun is properly aligned. :sometimes occurs thatthe control grid 11 and second grid .12, which usually are assembledtogether prior to the :assembly with the anode 13, are displaced withrespect Ito the axis of the rear portion of the anode 13, causing thebeam 36 to take a different path through the focusing .Slens for eachvariation of the magnetic ion-trap field 144 :from the assignedposition. In order that the electron beam 36 may pass properly throughthe focusing lens, it :may be necessary to tilt the lens. For example,if grid ,11 and second grid 12 are displaced by about 12 mils, a tilt ofthe entire focus lens assembly of about 1% is necessary to cause theelectron beam to coincide with the :axis of the focus lens aperture.Since this small angle is less than the angle of the tilted gun shown inFigure 4, the term substantially aligned applies equally to bothstructures.

Figure 6 shows another modification of the electron lens structure tothe right of line 33. Instead of a tubular field-defining electrode, aplane apertured disc 124 may be used. The focusing electrode 21 cannotoverlap the disc 124, but since this disc has a large diameter and, asin all other modifications, as illustrated in Figure 2, is directlyelectrically connected to the anode 13, the field in the lens regionwill be quite well-defined by the structure, particularly since theoverlap is retained at the anode 13 of the focusing electrode 21. Byproper design in accordance with well known principles, the aperturedcap 117 may be omitted, leaving only the tubular portion of the anode13.

The complete focusing structure shown in Figures 1 and 2 has been founddesirable in practice although certain simplifications are possible.Figure 7 shows the same structure without the extra disc 19 and here theaperture 18 in the cap 117 is used as the limiting aperture for theelectron beam 36. The structure shown in Figure 7 does not have quite asgreat reduction of secondary electrons as the structure shown in Figures1 and 2, unless somewhat greater care is taken in construction thereof.

The construction shown in Figure 8 is similar to that shown in Figure 7except that the caps 117 and 127 are plane instead of dish-shaped.

Figure 9 shows potential variation curves for the two structures inFigures 7 and 8 in which the spacings have been adjusted so that thefocal strength will be the same. The curve 46 may be seen to have asmaller slope in the region of the aperture 18 of Figure 7 than thecorresponding slope of curve 47 in the region of the correspondingaperture 118 as indicated at the points 48 and 49 respectively. Thus,the concave construction in .Figures 1, 2 and 7 appears to be beneficialin that it removes the apertures from the high gradient fields.

While the focusing electrode is shown connected to the "cathode, it maybe connected to other sources of poten- :tial including those outsidethe tube.

In practice, however, it,

This invention has been illustrated together withoiily a. fewmodifications. Other modifications may be apparent to those skilled inthe art without departing from the scope of the invention.

What is claimed is:

1. An electron discharge device comprising a bulb having a neck and atarget opposite said neck; an electron gun mounted Within said neck,said electron gun comprising in order along the path of the electrons,an electron emitting cathode, a control grid, a second grid, atcylindrical anode electrode having a concave apertured closuremember atthe end distal from said cathode, a cylindrical focusing electrodesubstantially axially aligned with said anode and overlapping saiddistal end; a cylindrical field defining electrode having the samediameter as said anode and having a concave apertured closure member atthe end facing said anode, and a conductive connection between saidanode and said field defining electrode; a conductive coating on theinternal wall of said neck, said conductive coating overlapping saidfield defining electrode; and a conductive connection between saidconductive coating. and said field defining electrode.

2; The device of claim 1 in which there is an angle between the axis ofsaid cylindrical anode and the axis of said field defining electrode.

3. The device of claim 1 in which said anode has a bend therein.

4. A cathode ray tube comprising a cathode for emitting electrons alongan electron beam path; an electron beam focusing lens structure throughwhich said path passes, said structure comprising in order a firsttubular anode electrode having a concave apertured closure member at theend remote from said cathode; a second tubular focusing electrodeoverlapping said remote end of said anode and electrically insulatedtherefrom; a tubular field defining electrode having an aperturedclosure member at the end closer to said anode, said focusing electrodealso overlapping said end of said field defining electrode; a pluralityof structures to support said anode, said focusing electrode,.and saidfield defining electrode in fixed rnechanical relation, each of saidstructures comprising an insulating support rod extending generallyparallel to said beam path; a first metal post having one end afiixed tosaid anode and the other end affixed to said rod; 2. second metal posthaving one end atfixed to said focusing electrode and the other endaifixed to said post; and a third metal rod having one end aifixed tosaid field definingelectrode and the other end afiixed to said rod, eachof said posts being so located that the distance along said rod from onepost to another is greater than the shortest space path between one ofsaid electrodes and another; and a direct electrical connection withinsaid tube between said anode and said field defining electrode.

5. The device of claim 4 comprising the radially outwardly extendingflange at the end of said field defining electrode remote from saidanode; and spring support means attached to said flange.

6. The device of claim 4 in whichsaid third tubular electrode has thesame diameter as said first tubular electrode.

7. The device of claim 4 in which both said closure members aredishshaped with the concave faces thereof facing each other.

8. An electron lens structure comprising a first tubular electrode; aconcave apertured closure member at one end of said electrode; a tubularfocusing electrode overlapping said end of said first electrode,insulated therefrom, and substantially aligned therewith; a thirdtubular electrode substantially aligned with said focusing electrode,insulated therefrom, and having a concave apertured closure member atthe end facing said first tubular electrode, said focusing electrodealso overlapping said third tubular electrode; and a conductiveconnection between said first tubular electrode and said 'third tubularelectrode.

, "9. The electrode structure of claim 8 in whichthe 2D than theexternal diameter of said proximal, ends, and

said focusing electrode overlaps said first and third electrodes each byan amount C where C is at least equal to D. I

1 0. In a cathode ray tubehaving a conductive coating on the wallsthereof, and a cathode, an electrostatic lens system comprising, incombination, three electrically insulated coaxial electrode members,said members including an intermediate cylinder and a pair of endcylinders, each said end cylinder having a portion received within saidintermediate cylinder, a1 direct electrical connection between said endcylinders, means to electrically connect one of said end cylinders tothe coating whereby a potential applied to said coating is present atboth said end cylinders, and means to supply a lower potential to saidintermediate cylinder to establish an electrostatic field between saidintermediate cylinder and each said end cylinder.

11. In a cathode ray tube having a-conductive coating on the wallsthereofand a cathode, an electrostatic lens system comprising, in:combination, three electrically insulated coaxial electrode members,said members including an intermediate cylinder and a pair of endcylinders, said end cylinders having a portion received within saidintermediate cylinders, a direct electrical connection between said endcylinders, means to electrically connect one of said end cylinders tothe coating whereby a potential applied to said coating is present atboth said end cylinders, and means to electrically connect saidintermediate cylinder to the cathode to apply the, same D.C. potentialto said cathode as is present atzsaid interj mediate cylinder to producean electrostatic field between said intermediate cylinder and each saidend cylinder.

12. The combination of claim 11 wherein the received portion of each endcylinder is terminated in an apertured.

reentrant convex end wall.

13. An electron lens structure comprising a first tubular electrode, aconcave apertured closure member at one end of said electrode, a secondtubular electrode overlapping said end of said first electrode,insulated therefrom, and substantially aligned therewith, a thirdtubular electrode substantiallyaligned with said second electrode,insulated therefrom and having a concave japertured closure member atthe end facingjsaid first tubular electrode, said second electrode alsooverlapping said Y third tubular electrode. V ,14. An electron lensstructure comprising a first tubular electrode, aconcave aperturedclosure member at the end of said electrode, a second tubular electrode'overlappinglsaid end of said first electrode and being substantiallyaligned therewith, a third tubular electrode References Cited in thefileofthis patent or. fthe 'original patent V UNITED STATES PATENTSRudenberg Oct. 27, 2,070,319 Rudenberg Feb. 9, 193 7 2,123,011 Keystonet a1. July 5, 1938 2,152,825 Schlesinger Apr. 4, 1939 2,163,210'Weinecke June 20,1939 2,191,415 Schlesinger Feb. 20, 1940 2,211,613Bowie Aug. 13, 1940 2,248,558 Schlesinger July 8, 1941 2,277,414 RamoMar. 24, 1942 2,363,359 Ramo Nov. 21, 1944 2,389,903 Hahn Nov. 27, 19452,452,893 Bachman Nov. 2, 1948 2,452,919 Gabor Nov. 2, 1948 2,454,345-Rudenberg Nov. 23, 1948 2,484,721 Moss Oct. 11, 1949 2,555,850 GlyptisJune 5, 1951 2,562,242 Pohle et a1. Ju1y 31, 1951 2,562,243 Pohle et'al, July 31, 1951 2,596,508 Phillipset' al. May 13, 1952 2,617,060 DeGier Nov. 4, 1952 2,732,511 -Dichter Jan. 24, 1956 OTHER REFERENCESArticle by Bowie, Proceedings of the Institute of Radio Engineers, pages1482-1486, vol. 36, No. 12, December 1948.

Industrial Electronics and Control, by R. G. Kloefiier, copyright 1949,published by John W. Wiley & C0., page 453, Fig. 2.

